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Diffstat (limited to 'src/tools/clippy/src/docs/derive_ord_xor_partial_ord.txt')
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diff --git a/src/tools/clippy/src/docs/derive_ord_xor_partial_ord.txt b/src/tools/clippy/src/docs/derive_ord_xor_partial_ord.txt new file mode 100644 index 000000000..f2107a5f6 --- /dev/null +++ b/src/tools/clippy/src/docs/derive_ord_xor_partial_ord.txt @@ -0,0 +1,44 @@ +### What it does +Checks for deriving `Ord` but implementing `PartialOrd` +explicitly or vice versa. + +### Why is this bad? +The implementation of these traits must agree (for +example for use with `sort`) so it’s probably a bad idea to use a +default-generated `Ord` implementation with an explicitly defined +`PartialOrd`. In particular, the following must hold for any type +implementing `Ord`: + +``` +k1.cmp(&k2) == k1.partial_cmp(&k2).unwrap() +``` + +### Example +``` +#[derive(Ord, PartialEq, Eq)] +struct Foo; + +impl PartialOrd for Foo { + ... +} +``` +Use instead: +``` +#[derive(PartialEq, Eq)] +struct Foo; + +impl PartialOrd for Foo { + fn partial_cmp(&self, other: &Foo) -> Option<Ordering> { + Some(self.cmp(other)) + } +} + +impl Ord for Foo { + ... +} +``` +or, if you don't need a custom ordering: +``` +#[derive(Ord, PartialOrd, PartialEq, Eq)] +struct Foo; +```
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